This invention relates to a hydraulic circuit, in particular for a clutch. More particularly, it relates to a receiver device which is adapted to receive control information from a hydraulic circuit in the form of pressure variations, being more precisely a receiver of the concentric type.
Receiver devices of this kind are for example described in French patent No. 82 03485 published under the No. FR-A-2 522 757.
Such receivers generally comprise, firstly, a fixed part consisting of an external body and a guide tube which are cylindrical and coaxial with each other, and secondly, a piston which is mounted for sliding movement coaxially with the fixed part, and which defines therein a variable volume chamber adapted to be connected to the hydraulic emitter of the hydraulic control system.
In traditional concentric clutch receivers, the guide tube has a transverse flange which is assembled by seaming to the external body of the receiver. This arrangement involves risks of fracture of the seamed joint due to the pressure prevailing in the variable volume control chamber, if the force on the casing is removed. In general terms, the body is made of an aluminium based material, and seaming makes it brittle.
As to the invention, this envisages a receiver for a hydraulic circuit of this type which is able to overcome these disadvantages.
According to another object of the invention, the receiver is made both simple and cheap.
To this end, the invention proposes a receiver of the concentric type for a hydraulic control system, comprising, firstly, a fixed part consisting of an external body and a guide tube which are cylindrical and coaxial with each other, and secondly, a piston which is mounted for sliding movement coaxially with the fixed part, and which defines therein a variable volume chamber adapted to be connected to the hydraulic emitter of the hydraulic control system, the external body including, on its inner face, a groove in which there is inserted a radial edge which is formed in the guide tube at one of its ends, and which partially constitutes the base of the variable volume chamber.
It will be understood that the use of a guide tube grooved in this way enables the problems of seaming and embrittlement of the material, posed by the traditional method, to be removed while guaranteeing very good sealing of the variable volume chamber of the receiver and providing good strength against pressure. Such a grooved tube enables the intermediate stop member of the radial flange of the guide tube, described in the document FR-A-2 754 030, to be eliminated, so that the invention is inexpensive. In addition, there is no need to create any weakening whatever in order to perform the seaming operation as described in the document FR-A-2 754 030.
Preferably, the guide tube includes a cylindrical portion having a flare defined by a conical portion which terminates in the annular edge inserted in the groove of the external body.
This arrangement increases the strength of the guide tube against mechanical forces linked to pressure, and facilitates insertion of the tube into the groove of the external body. It also reduces the axial size of the guide tube and facilitates supply of fluid to the chamber.
In a preferred arrangement, the external body has a tubular portion and a collar portion within which the groove is formed.
So as to permit the grooved tube to be force-fitted, the annular edge of the guide tube is preferably of a diameter which is slightly greater than the diameter of the inner face of the external body.
In order to improve the sealing of the fitting of the guide tube in the groove in the external body, the receiver preferably includes an O-ring seal disposed at the base of the groove between the external body and the edge of the guide tube.
The invention makes good use of tooling which consists of a backing tool for fitting the fixed part of the concentric receiver, of generally cylindrical form and having a lateral face which consists of a frusto-conical segment and an annular segment.
Thus, a method of fitting the fixed part, using a backing tool such as that mentioned above, comprises steps of placing the guide tube in the axis of the external body, holding the annular edge of the guide tube in contact with the shoulder of the external body using the backing tool, and varying the angle of the conical portion using a punch, so as to bring the annular edge into the groove.
In accordance with another arrangement of the invention, the fixed part includes a feed inlet which is joined to the collar of the external body. The feed inlet is open through an aperture disposed in the inner face of the external body and formed substantially facing the conical portion of the guide tube. In this way; easier flow of the hydraulic fluid into the variable volume chamber of the receiver is obtained, while the latter is being put under pressure. It will be appreciated that this type of use with a grooved guide tube is applicable to a large number of receivers, in particular those described in the documents FR-A-2 754 030, FR-A-2 757 590. Because of the frusto-conical portion of the guide tube, the seal associated with the piston may be in the form of a toroidal cup which comes very close to the frusto-conical portion when the clutch is engaged.
Thus, in one embodiment, the head of the piston comprises at least two segments assembled in an annular arc by virtue of a positioning means and an annular ring carrying the said seal. This arrangement enables a piston head of complex cross section to be formed by moulding, and then to be assembled with a matching means, without being limited by the constraints imposed by stripping from the mould. The seal is a connector for assembling the segments together. Thus, thanks to the invention, a hydraulic receiver is obtained which is simple to make and of low selling price, which to this end requires in particular less machining than in the traditional method and is preferably made of light material.
In order to enable the piston head to be assembled with the other components of the concentric receiver, the segments in an annular arc have a step flange on their rear face.
In one embodiment, by virtue of these arrangements, the piston has a protective skirt terminated by an external lip seal, the form of which is adapted to slide on the tubular portion of the external body of the receiver.
This arrangement enables the conventional protective bellows to be omitted, and thereby simplifies assembly of the concentric receiver, while guaranteeing good protection for the piston against the entry of dust.
This arrangement is applicable to any kind of receiver of the concentric type, but it goes very well with the use of a guide tube which is grooved, because good concentricity is obtained between the guide tube and the external body, which limits the risk of jamming in the region of the lip seal of the protective skirt.
Accordingly, the receiver may include a cylindrical piston support tube which is terminated by an annular flange on the same side as the variable volume chamber, the said piston support tube being of a metallic nature and being mounted around the guide tube, with a means being provided for fixing the piston around the said piston support tube.
Thanks to this arrangement, there is separation of the functions between, firstly, that of supporting deformations due to temperature and mechanical forces due to the assembly means, and secondly, the function of transmission of thrust from the piston to the declutching member, namely the clutch release bearing.
The metallic piston support tube takes the thermal and mechanical forces from the assembly means, while the piston is so dimensioned as to transmit only the pressure forces.
The means for assembling the piston around the piston support tube is preferably an elastic autocentring ring in engagement on the piston support tube, such as is associated with a so-called autocentring clutch release bearing.
This simplifies assembly of the whole.
The autocentring ring is preferably in the form of a frusto-conical annular ring and has deformable nibs. The piston support tube has a shallow groove formed in its front end and arranged to receive the deformable nibs of the autocentring ring. In a preferred arrangement, the shallow groove of the piston support tube has a front flank which is inclined at a slope of about 45xc2x0. In a particular arrangement, the deformable nibs of the autocentring ring define a dihedral with the frusto-conical annular ring portion of the said autocentring ring.
In order to simplify its manufacture and reduce its selling costs and its weight, the piston is preferably made of plastics material.
The piston includes structural reinforcing ribs oriented in a direction substantially parallel to the axis of the piston. This arrangement enables a geometry to be chosen for the piston which gives it good structural strength, while forming apertures which reduce the material used and overall weight.
In a preferred arrangement, the receiver includes a lip seal placed around the guide tube under the piston support tube.
The lip seal is extended by a set of lugs constituting guide pads, which are carried by the guide tube and disposed under the piston support tube.
These arrangements facilitate movement of the piston support tube. The piston support tube, in combination with the piston, is thermally insulated.
In a preferred arrangement, the guide pads are six in number, each one subtending an angle of approximately 50xc2x0, and separated by a sector of 10xc2x0 of angle along the guide tube.
It will be understood that in this way, any problems of thermal expansion are reduced, and that as a consequence, an arrangement which reduces vibrations is obtained.
Preferably, the guide pads terminate at their ends remote from the lip seal in radial flanges. This facilitates assembly of the guide pads with the piston head.
The guide pads and the lip seal are preferably made of plastics material. All of these arrangements are applicable to other types of receivers, but they are very well suited to the use of a type with a grooved guide, due to the good concentricity of the guide tube and small deformations of the guide tube under the effect of pressure variations. Further features of the invention will appear on a reading of the description and claims that follow.